1. Field of the Invention
The present invention relates to a display apparatus having a plurality of display devices by which a single image is displayed.
2. Description of the Related Art
Generally, with a display apparatus there are various factors which determine visual comfort, such as brightness, contrast, whiteness, blackness, color range, screen size, and other visual characteristics. Among various types of display apparatuses, a liquid crystal display (LCD) apparatus is superior to others in brightness, contrast, whiteness and blackness, considering its small consumption of electricity and its ability to be driven by a low voltage. Moreover, the LCD apparatus can relatively easily provide a color display. The LCD apparatus can be constructed in a flat panel, and hence has an advantage that the thickness (i.e., depth) of the apparatus can be made considerably smaller than that of a conventional cathode ray tube (CRT). As a result, the LCD apparatus is becoming more popular in various fields of use.
Such an LCD apparatus has a structure in which liquid crystal is confined between a pair of substrates facing each other at a distance on the order of microns and having transparent electrodes thereon. Therefore, if fine dirt, dust or the like is mixed into or becomes adhered to the inside of the apparatus during the production process, the dirt or dust prevents the apparatus from operating properly. In particular, faulty picture elements are more likely to occur. In addition, due to the above-mentioned structure, a larger screen size has a higher probability of there being an occurrence of fault picture elements, i.e., the fault rate of a display apparatus having a larger screen size is higher. As to an LCD apparatus in which such faulty picture elements occur, the display quality is largely deteriorated. Therefore, the LCD apparatus is disposed or discarded.
As described above, in an LCD apparatus, a larger screen size results in a higher fault rate due to faulty picture elements. Especially when the screen size is on the order of 15 inches or larger, it is very difficult to mass-produce such an LCD apparatus at reasonable production costs.
In order to overcome this problem, a plurality of minor LCD devices having a screen size of 15 inches or smaller are arranged lengthwise and widthwise in an array pattern, so as to constitute a single LCD apparatus having a large display area. An example is shown in FIG. 1A. In FIG. 1A, nine minor LCD devices 1 are arranged in a 3.times.3 array. With this construction, if each minor LCD device 1 is, for example, of a 14-inch square type, the screen size of a resulting large-sized LCD apparatus 2 will be approximately 42 inches by 42 inches.
However, each of the minor LCD devices 1 have a non-image area 1b on which an image is not displayed along the periphery of a display area 1a on which an image is displayed, as is shown in FIG. 1B. For example, the non-image area 1b having a width of at least 3 millimeters (mm) is formed by a space for containing the liquid crystal confined between the two opposing substrates, and a space for disposing wiring and the like for applying a voltage to the minor LCD device 1 so as to drive the picture elements.
Accordingly, as is shown in FIG. 1A, the resulting LCD apparatus 2 has the non-image areas 1b in a shape of a lattice surrounding the respective display areas 1a, i.e., the display area of the resulting LCD apparatus 2 is discontinuous (by seams). As a result, the display quality is deteriorated and therefore the displayed image may be erroneously displayed and/or viewed.
In order to solve the problem mentioned above, a display apparatus has been proposed in Japanese Patent Application No. 3-293425 by the inventors of the present invention. According to this display apparatus, a single display area is formed by a plurality of display devices, and an image can be displayed on the display area without discontinuity. A fundamental structure of such a display apparatus is shown in FIG. 2.
The proposed display apparatus includes, for example, two display devices 11 and 12 provided with display areas 11a and 12a, respectively, juxtaposed along a direction A, as is shown in FIG. 2. To each of the display areas 11a and 12a, end faces D of optical fiber bundles 3 for transmitting an image are connected. On the other end faces C of the optical fiber bundles 3, a composite image having no boundary area appears. Each optical fiber bundle 3 is made up of a plurality of parallel optical fibers 3' which are bent at an angle .theta..sub.1 at a predetermined point (a point E in FIG. 2). In the display apparatus shown in FIG. 2, the display devices 11 and 12 are separately formed, but in another case, display devices 13 and 14 may be adjacently formed, as is shown in FIG. 3.
In the display apparatus shown in FIG. 2, an image signal representing an image which is displayed on the display areas 11a and 12a of the display devices 11 and 12 is introduced into the optical fiber bundles 3 at their one end faces D, transmitted through the optical fiber bundles 3, and emitted from the other end faces C.
A method of forming the optical fiber bundles 3 is now described. First, as is shown in FIG. 4, optical fibers 31 having the same length are arranged side by side, and are then fastened to each other so as to form an optical fiber sheet 32. Next, as is shown in FIG. 5, the optical fiber sheet 32 is bent in a direction perpendicular to away from the arranged direction of the optical fibers 31 so that the portions of the optical fiber sheet 32 on the sides of the introducing end face D and the emitting end face C form a bent angle .theta..sub.1. Thus, a bent optical fiber sheet 33 is formed. A plurality of bent optical fiber sheets 33 are stacked in a direction in which the optical fiber sheet 32 is bent, so as to form the optical fiber bundle 3 as a unit of the display area 11a or 12a.
Referring briefly to FIG. 3, each optical fiber bundle 3 has an outward facing slope 3c and an inward facing slope 3d on opposing side faces of the stacked bent optical fiber sheets 32. The emitting end faces C of the optical fibers 31 which form the optical fiber bundle 3 are made flat, and the optical fibers 31 are arranged at regular pitches.
FIG. 6 shows a partial sectional view of the optical fiber bundle 3. Each of the optical fibers 31 making up the optical fiber bundle 3 has a core portion 31a and a clad portion 31b which has a lower refractive index than that of the core portion 31a. The optical fibers 31 are fixed to each other using a suitable adhesive 34.
Finally, two optical fiber bundles 3 constructed in the above-described manner are joined so as to form a display apparatus. At this time, the optical fiber bundles 3 are joined so that the outward facing slopes 3c thereof do not interfere with each other. For this reason, the optical fiber bundles 3 preferably are joined such that vertical side faces 3e extending from the inward facing the side of the slopes 3d are connected.
With the above construction, a display apparatus having a display area double the size of the display area 11a (12a) of one display device 11 (12) can be obtained. The two display devices 11 and 12 are driven through a driving circuit (not shown) using split signals. The split signals are obtained by splitting an image signal for each frame into two signals, e.g., a corresponding signal for the right and left fields. Therefore, the image appearing on the display areas 11a and 12a is displayed as a composite image on the emitting ends faces C of the combined optical fiber bundles 3 without discontinuity.
The number of the display devices which are joined is not limited to two, and a resulting display apparatus may be formed by three display devices joined in a direction A, as is shown in FIG. 7. In this display apparatus, an optical fiber bundle 35 which is not bent is interposed and joined between the two optical fiber bundles 3 which are bent in the same way as in the above example having two display devices. With such a construction, a thin display apparatus having a display area three times the size of a display area 15a (16a, 17a ) of one display device 15 (16, 17) is provided. However, it is difficult to join four or more optical fiber bundles 3 because the outward facing slopes 3c on the introducing end face side interfere with each other. Also, it is difficult to add another optical fiber bundle 3 in a direction B perpendicular to the direction A. If there exists no non-image area 1b, a number of display devices can be joined with each other. However, as described above, since a resulting display apparatus unavoidably has the non-image areas 1b, it is substantially impossible to realize such joining.
Regarding the bent angle .theta..sub.1 of the optical fiber bundle 3, when the angle .theta..sub.1 is small, a distance L (FIG. 1) between the introducing end face D and the emitting end face C is long. Therefore, it is required to make the bent angle .theta..sub.1 larger in order to realize a thin display apparatus. However, according to the above-described approach, it is difficult to make the bent angle .theta..sub.1 larger without disordering the arrangement of the optical fibers 31.
In the above display apparatus, the emitting end face C of the optical fiber bundles 3 for transmitting an image signal is made even, so that the viewing angle corresponding to the emitting angle of the optical fiber bundle 3 is small. As a result, the display apparatus has a disadvantage that if the viewing angle with respect to the display screen is changed only a little, the displayed image cannot be seen.
There are methods for enlarging the viewing angle including a method of roughening the emitting end face C of the optical fiber bundle 3, a method of making the emitting end of each of the optical fibers 31 into a lens-like shape (Japanese Laid-Open Patent Publication No. 60-169833), and a method of disposing a scattering plate or a microlens array sheet on the emitting end face C of the optical fiber bundle 3 (Japanese Laid-Open Patent Publication No. 1-189616). However, although the viewing angle can be enlarged by the roughening method for the optical fiber bundle 3 and the method of forming a scattering plate, the light from the outside is more largely scattered on the display screen as the visual angle is enlarged. This causes a problem in that the displayed image is whitish and the image quality is deteriorated. By the method of disposing a microlens array sheet, the microlens array sheet is expensive, thereby disadvantageously increasing the production cost. By the method of making the end of the optical fiber into a lens-like shape, the process is difficult to perform, whereby production efficiency decreases. As mentioned above, any one of the conventional methods cannot satisfactorily attain the purpose of enlarging the viewing angle.
Moreover, there exists another problem in that the arrangement of the optical fibers 31 is disordered when the optical fiber bundle 3 is produced. Especially with respect to the method of disposing a microlens array sheet, it is important to align the optical fibers 31 and the microlens array. Accordingly, it is difficult to use the method with the disarranged or disordered optical fibers 31 in combination with the microlens array.
In addition, as is seen from FIG. 6, in the optical fiber bundle 3, the core portions 31a occupy a relatively small volume of the optical fiber bundle 3 due to the presence of the clad portions 31b and the spacing between respective clad portions. Since light which is introduced into the clad portions 31b is not transmitted, this causes a problem in that an image appearing on the emitting end face C is dark and the image quality is deteriorated.
Moreover, the end faces C of the optical fiber bundle 3 are always exposed to the air. The core portion 31a of the optical fiber 31 is made of acrylic, so that the core portion 31a tends to absorb moisture in the air from the exposed ends and to expand and shrink repeatedly. Because of this, the optical fiber bundle 3 may be cracked, and hence the displayed image quality may be distorted. A small gap unavoidably occurs between the periphery of the introducing end face D of the optical fiber bundle 3 and the periphery of the display device 11, 12, . . . . In some cases, fine dirt may enter from the small gap. This partially prevents an image signal from transmitting, and faulty picture elements occur in the display area 11a, 12a, . . . of the display device 11, 12, . . . Sometimes, the acrylic core portions 31a may absorb moisture from the small gap, which causes the optical fiber bundle 3 to be cracked. As a result of such faulty picture elements and the crack of the optical fiber bundle 3, a black line or lines appears on the screen, which degrades the reliability and durability of the display apparatus.